Air-conditioning method and apparatus with heat pump

ABSTRACT

To prevent icing on the vaporization surfaces of the condenser in a heat pump air-conditioning system, the temperature of the air in contact with the condenser is raised by applying additional heat thereto, for example by an electric heating coil, bleeding of fresh air, or feedback of heated air.

United States Patent 91 Carrasse et al.

[451 Feb. 25, 1975 AIR-CONDITIONING METHOD AND APPARATUS WITH HEAT PUMP Inventors: Jean Carrasse, Antony; Denise Desbrosses, Villemoisson s/Orge, both of France Societe Generale de Constructions Electriques et Mecaniques (Alsthom), Paris, France Filed: July 6, 1971 App]. No.: 159,681

Assignee:

Foreign Application Priority Data July 7, 1970 France 70.25409 US. Cl 165/29, 165/2, 62/325, 62/275, 62/89, 62/79 Int. Cl. F25b 29/00 Field of Search 165/2, 29, 64; 62/159, 62/325, 262, 275, 79; 237/2 B References Cited UNITED STATES PATENTS 12/1940 Morrison 62/262 FOREIGN PATENTS OR APPLICATIONS 103,682 4/1938 Australia..... 62/325 Primary ExaminerWilliam J. Wye Attorney, Agent, or Firm-Flynn & Frishauf [.57] ABSTRACT Toprevent icing on the vaporization surfaces of the condenser in a heat pump air-conditioning system, the temperature of the air in contact with the condenser is raised by applying additional heat thereto, for example by an electric heating coil, bleeding of fresh air, or feedback of heated air. v

5 Claims, 3 Drawing Figures PATENTED FEB2 5l975 SHEET 1 a; 5

FIG/l AIR-CONDITIONING METHOD AND APPARATU WITI-I HEAT PUMP The present invention relates at a process and an apparatus for air-conditioning of an enclosed space, for example residential, commercial or plant space, utilizing a heatpump cycle. When the interior temperature isless than the desired value, a heat exchange fluid is condensed with exterior air entering the space, and the heat exchange fluid is expanded and vaporized and heat is then exchanged with the air leaving the space; whereas, when the interior temperature is higher than the desired value,- the heat exchange fluid in the cycle is condensed by heat exchanging air leaving the space and the vaporization, or expansion heat exchange is carried out with exterior fresh air being supplied, or with air being recirculated. I

Known processes of air-conditioning, that is, maintaining a certain temperature level, utilizing a heat pump, operate on comparatively low pressure gaps between the condenser and the vaporizer, or expansion unit of the fluid in the cycle. It may occur that the evaporator is subject to frosting, or icing, particularly when the temperature of the fluid being vaporized drops to -3 C, or less. Icing of the equipment greatly decreases the heat exchange coefficient of the evaporator. lf icing occurs, it is necessary to interrupt theheat pump cycle for periodic defrosting. It has been proposed to use an auxiliary heat source, during this interruption of the heat pump cycle. Interruption of the heating of the interior space, in order to permit additional heating of the evaporator interferes with the efficiency of the apparatus as a total, year-round air-conditioning unit particularly in regions which have relatively severe winters.

Two temperature zones of exterior, ambient temperatures may be distinguished. These two zones are separated by a temperature level which may be termed a critical temperature, below which the power necessary in order to maintain the space at the desired temperature, due to heat losses of thespace and necessary reheating of the air to bev ventilated, is greater than the power which can be supplied by the compressor of the cycle, When the outside temperature is higher or greater than the critical temperature, then it is possible to operate the. cycle .without icing and without additional heating by an external source ofheat, since power supplied and heat losses will be, or can be maintained to be in balancelf, however, the exterior temperature is less than the critical temperature, additional heat energy must be supplied to restore the balance, for example by means of an auxiliary heating unit, such as one or more electrical resistance units.

temperature. The three embodiments may be used in It is an object of the present invention to overcome the disadvantages of known heat pump cycles by providing for operation of the heat pump evaporator under such condition that it will not ice, even if the outer side ambient temperatures drop substantially below freezing, that is below 0 C. The heat pump cycle is to operate economically, regardless of outside temperatures, and continuously so that the temperature being maintained in the space to be controlled will be little different regardless of outside temperatures. The heat energy being supplied should be efficiently utilized and permit different rates of ventilation and heat losses, as well as choice of interior temperature to be maintained; the heat pumps themselves should be capable of supplying sufficient heat while being of essentially uniform con- SUBJECTMATTER OF THE PRESENT INVENTION Briefly, the mean temperature of air in contact with the condenser is artifically increased over the mean temperature which would result from heat exchange by the condenser with air at outside temperature entering the space to be heated during those period of time when the vaporization temperature of the heat exchange fluid, in heat exchange with'the air leaving the space, is sufficientlylow to be subjected to risk of icing of the heat exchange surface, itself. 3

The mean temperature of the air in contact with the condenser can be raised by various means; in accordance with one-embodiment, an external, separate and independent heat source isprovided, preferably an electrical resistance unit; in accordance with anohter embodiment, a portion of the exterior air is bypassed and reunited with a portion of the air which passed the condenser, so that the condenser received additional heating by thelesser amount of heat being removed, due to the bypass; or, a portion of the heated air which already has contacted the condenser is rel-cycled and fed back to the condenser unit itself to pre-heat the air entering into the condenser, thus supplying additional heat to the condensing heat exchange step. The latter two embodiments, in ,which no additional heat is supplied, which is a cost factor, are applicable when the outside ambient temperature is not less than the critical combination and, particularly, the first embodiment can be combined with either the second or third, the method. and apparatus of the first embodiment being placed in operation only when the outside temperature drops belowthe critical temperature.

The inventionwill be described by way of-example with reference to the accompanying drawings, wherein; FIG. 1 is a schematic diagram ofa heat pump installationlutilizing electrical resistance elements to supply additional heat; v 1

FIG. 2 is a schematic diagram ofaheat-pump installa-- tion utilizing'bypass of fresh air; and J FIG. 3 is a schematic diagram ofaheat pump installation using a re-cycling feedback of heated air.

In all three installations of the drawings, the upper portion of the Figures represents the space to be temperature controlled, and'the lower portion of the Figures represents outside ambient atmosphere.

Embodiment of FIG. 1: A compressor] compresses the heat exchange fluid, such as a refrigeration fluid for example known under the tradename FREON (a fluorinated hydrocarbon) having a low boiling point at'atmospheric pressure. Other heat exchange fluids may be used, such as ammonia or sulphurous anhydride. The compressed heat exchange gas is conducted over pipes 2 to a condenser 3. The heat exchange gas liquefies in condenser 3, and, in the process, heats the air which is supplied from the outside atmosphere to the interior of the conditioned spacae. The heat exchange fluid is then applied over pipe 4 to expansion valve 5, where the liquefled gas expands and passes over pipe 6 into evaporator 7 where it will vaporize, in the process cooling and de-humidifying used air being exhausted from the space to be temperature controlled and ventilated. The heat exchange fluid is led back to the suction side of the compressor over pipe 8.

Air is exhausted from the conditioned space by a fan or exhaust ventilator 10 located in an air duct 9. It is cooled and de-humidified by contact with the evaporator 7. Condensation water is removed by mens well known in the art and not shown in the drawing. Fresh air is introduced into the space to be controlled by a fan or ventilator 12 located in a duct 11.

Duct 11 includes an electrical resistance unit 13 which provides for a first pre-heating of air before it comes in contact with condenser 3. The pre-heated air, after contacting the condenser, may be subjected to additional heating to reach the desired temperature of air to be introduced in the space, usually at least 35 C. Additional heaters l4, 15, which are electrical resistance heating units and which may be similar to unit 13 are provided to complete further heating ifthe outside temperature is very low. For example, the energy supplied by the resistance heating unit 14 may be calculated to provide for a desired temperature of air being introduced into the space when the outside temperature drops to about -C; the energy supplied by resistance 15 then may be calculated to assure heating if the temperature drops by another 5, that is, when the outside temperature is about C, both resistances 14 and are placed in circuit. Resistance 13 is connected when the temperature drops to close to freezing.

Embodiment of FIG. 2: The circuit of the heat exchange fluid is identical to that of FIG. 1 and will not be described again, and the same reference numerals have been used. The inlet heat duct 11', supplying fresh air, is formed with .a bypass line 16 in which a control valve or air flow regulator 17 is placed. As shown by the arrows, a portion of the air entering the duct 11, and drawn therethrough by ventilator 12 will flow through the bypass l6 and is then mixed with the major portion behind condenser 3. The mean temperature of the air being supplied at the outlet of duct 11'will thus be less than the temperature to which the condenser is subjected, thus increasing the temperature of condensation. In case of rapid drop of outside temperature, this device provides for fast compensation since no additional apparatus which may require starting or initial heating is necessary. Control of the valve 17 can be rapid. If the embodiments of FIGS. 1 and 2 are combined, then heating unit 13 can be placed either before, or behind the entrance of bypass 16, preferably between the entrance to bypass l6 and condenser 3. Heating unit 14, 15 can be located preferably downstream from the exit of bypass 16.

Embodiment of FIG. 3: The heat exchange fluid cycle is identical to that of FIG. 1, has been given the same reference numerals, and will now be described again. lnlet duct 11", through which fresh air is admit ted from the outside atmosphere has a re-cycling bypass 18 connected thereto, in which a control valve or air flow control blade 19 is installed. As seen by the arrows, re-cycling feedback duct 18 takes a portion of the air heated by the condenser and re-cycles it back to the advance of the condenser, for additional heat supply thereto. The amount of air passing the condenser is thus increased and is larger than the amount of air introduced into the space to be temperature controlled; the temperature at the inlet to the condenser is greater than that which the air would have in the absence of recycling; the temperature at the outlet of duct 11 is for all practical purposes unaffected. This form of the invention permits an increase of the temperature of the condensed heat exchange fluid, and thus an increase of the vaporization temperature and a ready means to avoid any risk of icing at the only costs of requiring a fan or ventilator 12 which is slightly more powerful than that necessary for the embodiment, for example, of FIG. 1,. or for a similar installation without the recycling arrangement formed of bypass and feedback tube 18 and the control element 19. if additional heat- 7 ing elements l3, l4 and 15 are to be used, they can be placed at any convenient position with respect to duct 18, for example elements 13 may be upstream from the exit of duct 18 and elements 14,15 may be downstream from the entrance to duct 18.

The additional air introduced could be mixed not only with air re-cycled downstream from the condenser, but also with air taken from the space to be temperature controlled. This also increase the input temperature of the air to the condenser, but only very slightly, since the difference in temperature between the exteriorair' and the air in the interior of the space to be controlled is not sufficiently great to substantially affect the vaporization temperature at the condenser.

. condenser is increased, such that the mean temperature of the air in contact with the condenser is notsufficiently increased to greatly affect the operation of the system. It is, therefore, a not generally satisfactory solution to utilize air from the space to be temperature controlled as a source for supplying additional heat to the condenser.

Various changes and modifications may be made within the scope of the present invention; specifically, air may be split or re-cycled, or applied to only aportion of the heat exchange surface of the condensers. The source of additional heat to be supplied need not be an electrical resistance wire, but may be obtained. from heat exchangers of any kind, boilers, gas or liquid heaters and the like. The heat pump cycle may be by compression and/or fractionated expansion. Rather than utilizing ambient air from the atmosphere, a portion of the ambient air may be taken from the space, to be re-cycled and when reference is made to fresh air being introduced, such air may be withdrawn, filtered and re-cycled back to the space which is to be temperature controlled, at least in part.

We claim: 1. Air-conditioning apparatus employing a heat pump of the kind continuously circulating air between a space to be conditioned and external ambient air and continuously performing inverse heat exchange operations relative to a refrigerant respectively on the intake air to said space and on the exhaust air therefrom, comprising a compressor, a condenser, and an evaporator c onnected in a closed circuit to form a heat pump and providing for the circulation of a refrigerant;

means included in said circuit between said condenser and said evaporator for the expansion of said refrigerant;

a first duct including air moving means for drawing exterior air over said condenser into an enclosed space;

a second duct including air moving means for the exhaust of interior air over said evaporator from said enclosed space;

and means included in said first duct for raising the temperature of condensation of said refrigerant within said condenser by reducing the cooling efnected to said first duct between the entrance thereof and said condenser and an outlet connected to said first duct beyond said condenser, and the air moving means of said first duct is positioned therein beyond the outlet of said bypass line; thereby to provide a bypass of said condenser for a part of the exterior air drawn into said a first duct.

5. Air-conditioning apparatus as defined in claim 1 wherein the temperature raising means comprises a bypass line, including a regulator. having an inlet connected to said first duct between the entrance thereof and said condenser and an outlet connected to said first duct beyond said condenser, and the air moving means of said first duct is positioned therein between said condenser and the outlet of said bypass line; thereby to recycle a part of the exterior air drawn into said first duct. 

1. Air-conditioning apparatus employing a heat pump of the kind continuously circulating air between a space to be conditioned and external ambient air and continuously performing inverse heat exchange operations relative to a refrigerant respectively on the intake air to said space and on the exhaust air therefrom, comprising a compressor, a condenser, and an evaporator c onnected in a closed circuit to form a heat pump and providing for the circulation of a refrigerant; means included in said circuit between said condenser and said evaporator for the expansion of said refrigerant; a first duct including air moving means for drawing exterior air over said condenser into an enclosed space; a second duct including air moving means for the exhaust of interior air over said evaporator from said enclosed space; and means included in said first duct for raising the temperature of condensation of said refrigerant within said condenser by reducing the cooling effect of the flow of exterior air over said condenser.
 2. Air-conditioning apparatus as defined in claim 1 wherein the temperature raising means includes an independent source of heat in said first duct between the entrance thereof and said condenser.
 3. Air-conditioning apparatus as defined in claim 2 wherein said independent source of heat comprises an electrical resistance.
 4. Air-conditioning apparatus as defined in claim 1 wherein the temperature raising means comprises a bypass line, including a regulator, having an inlet connected to said first duct between the entrance thereof and said condenser and an outlet connected to said first duct beyond said condenser, and the air moving means of said first duct is positioned thereiN beyond the outlet of said bypass line; thereby to provide a bypass of said condenser for a part of the exterior air drawn into said first duct.
 5. Air-conditioning apparatus as defined in claim 1 wherein the temperature raising means comprises a bypass line, including a regulator, having an inlet connected to said first duct between the entrance thereof and said condenser and an outlet connected to said first duct beyond said condenser, and the air moving means of said first duct is positioned therein between said condenser and the outlet of said bypass line; thereby to recycle a part of the exterior air drawn into said first duct. 